Adenoid cystic carcinoma (ACC), a rare malignant tumor in the head and neck, invades diffusely and easily metastasizes to the lung, although the growth rate is very slow. A retrospective study was conducted in 30 patients with ACC to ascertain the actual frequency of pulmonary metastasis, the tumor doubling time of metastatic tumors, and the onset of metastasis. The following results were obtained:
1) Of 30 patients with ACC, 21 had pulmonary metastases (4 initially and 17 during observation), 7 were free from metastases but not yet observed for 5 years, and 2 were free from metastases for 5 years or longer after initial treatment. The cumulative metastasis rates at 5 and 10 years were 70% and 100%, respectively.
2) Patients with T 1 or T 2 tumors and with histologic evidence of a tubular or cribriform pattern had pulmonary metastases about 20 months later than those with T 3 or T 4 tumors and with histologic evidence of a solid pattern, but the final metastasis rate did not differ between these groups after a prolonged period.
3) The tumor doubling time of metastastic tumors of ACC was 86 to 1064 days (mean, 393 days), which was much longer than that of most other malignant neoplasms reported previously.
4) The onset of pulmonary metastasis was calculated to be much earlier (mean, 227 months) than the time of initial therapy.
5) These findings indicate that treatment for ACC should take into account that most patients have pulmonary metastases at presentation.
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